1. Technical Field
The present invention relates energy storage devices using magnetic fields and a material, such as mu-metal, that can provide the property of screening or attenuating magnetic fields. More particularly, the present invention relates to components used in constructing an energy storage device, such as a fly wheel, using magnetic fields and mu-metal.
2. Related Art
Magnetic fields can be created by permanent magnets or electro magnets. The magnetic field generated can be used to create magnets to lift metal containers or scrap metal, to deflect charged particles as in a cathode ray tube, and to operate electric motors. Many uses for magnetic fields have been discovered, and it would be desirable to provide a means to enhance those uses or enable potentially untapped uses for magnetic fields.
Control of the electro magnetic field enables components such as magnetic lifting devices, charged particle deflectors, or electric motors to operate. For example, electric motors typically operate with a combination of permanent magnets arranged in a circle, and opposing electromagnets. Current is applied to the electromagnets in a manner to operate the device as an electric motor, or alternatively to use the device as a brake or charge generator. To provide an electric motor, current is applied to the electromagnets with appropriate timing so that the permanent magnets and electromagnets pull toward each other, and then push away from each other after passing to accelerate the motor in a desired direction. The electric motor can similarly be used for braking, such as regenerative braking used in hybrid electric-gasoline powered vehicles. To use the electric motor as a brake or generator, current is withdrawn from the electromagnets in a reverse direction of the current application to the electric motor so that the permanent magnets push away from each other and then pull toward each other after passing to decelerate the motor.
Mu-metal provides the property of high permeability making it very effective at screening static or low frequency magnetic fields, which cannot be attenuated by other methods. Its high permeability provides its “mu” name, with permeability being represented by μ the Greek letter mu. Mu-metal is a nickel-alloy, namely approximately 75% nickel and 15% iron plus a mixture of copper and molybdenum. The materials are annealed in a hydrogen atmosphere.
The annealing organizes the mu-metal's crystal structure so that its valence electrons are aligned in an arbitrary manner, unlike other magnetic materials. Permanent magnets have atoms with aligned valence electrons. In a soft metal such as iron the grains that do not normally have aligned valence electrons forming electromagnets, but current can be applied so that their valence electrons are aligned giving then a magnetic property. With mu-metal, the electrons will be arranged in a random manner so that no matter what the direction of a magnetic field applied to the mu-metal, its valence electrons will not align. This will cause a magnetic field striking the mu-metal to be significantly attenuated.